Method for activating a restraint system in a vehicle

ABSTRACT

A method for activating a restraint system in a vehicle, in which the restraint system is activated as a function of a speed, an activation characteristic, and at least one quantity derived from an acceleration signal, and in which the at least one quantity exceeds a threshold function that is set as a function of the impact speed and a required activation time. The activation characteristic of a particular accident type runs linearly to a first impact speed value. The activation characteristic runs with a second slope between the first impact speed and a second impact speed value, the first and the second impact speed value depending on the particular vehicle type.

FIELD OF THE INVENTION

The present invention relates to a method for activating a restraintsystem in a vehicle.

BACKGROUND INFORMATION

A method for activating a restraint system in a vehicle is discussed inpublished unexamined German patent application document no. 197 24 101.In this context, the crash severity is estimated from the impact speedand vehicle stiffness data is taken into consideration, activationultimately occurring as a function of a comparison of a thresholdfunction and an acceleration signal or a quantity derived therefrom. Thethreshold function is determined according to an activationcharacteristic determined from crash tests for the particular vehicle.

SUMMARY OF THE INVENTION

In contrast, the exemplary method of the present invention foractivating a restraint system in a vehicle, having the features of theindependent claim has the advantage that the activation times for quickand hard crashes are determined in an improved manner in accordance withthe requirements, the transferability of activation performance to crashtypes or accident types in particular being able to be ensured withfewer crash tests. The core of the exemplary method is that there is avehicle-dependent speed limit G after which a linear regression line nolonger effectively describes the activation performance of the airbag.These linear regression lines are identified in crash tests and areentered in a speed activation time diagram. In addition, there is avehicle-dependent speed after which the restraint arrangement, apparatusor structure is either activated at a fixed instant or is not activatedwithout detailed differentiation between the accident or crash type. Theexemplary method of the present invention allows for transfering theactivation performance from the knowledge of the activation performancein the lower speed range to the speed range between speed limit G andspeed P. This designates a speed range between 70 and 130 km/h, forexample.

It is believed that the measures and further refinements describedherein provide advantageous improvements of the exemplary method foractivating a restraint system described herein.

It may be particularly advantageous that the activation characteristicruns linearly between the first and the second impact speed value. Thecrash test performed at 15, 20, 25 to 70 km/h, for example, result in anactivation characteristic having linear properties. Activationcharacteristic refers to the function that defines the relationshipbetween impact speed and activation time for a given crash type. Everycrash type may have its own activation characteristic. The activationcharacteristics may result from the requirements of the vehiclemanufacturer. These requirements determine when the restraintarrangement, apparatus or structure, e.g. an airbag or a beltpretensioner, is to be activated in the event of a crash against a givenbarrier at a certain impact speed. In this context, crash and accidenttype refer for example to a front impact, an offset crash, a sideimpact, a rear impact, an impact against a hard barrier, an impactagainst a soft barrier, and a pole crash, as well as a rollover.Therefore, the accident type refers to the type of accident.

It may also be advantageous that a fixed activation time is usedstarting at second impact speed value (P). Starting at this impactspeed, the crash is so hard that the restraint arrangement, apparatus orstructure must be activated immediately.

Finally, it may also be advantageous that a device for activating arestraint system is provided with the exemplary method of the presentinvention, the device including in particular a control unit that isconnected to the corresponding sensors, e.g. a pre-crash sensor fordetecting the impact speed and an inertial sensor for detecting theacceleration during a crash. The control unit then controls therestraint system accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of the exemplary device of the presentinvention.

FIG. 2 shows an impact speed activation time diagram.

FIG. 3 shows a further impact speed activation time diagram.

DETAILED DESCRIPTION

To control the restraint arrangement, apparatus or structure in avehicle, the signal from an acceleration sensor or a plurality ofacceleration sensors is evaluated. The values for this signal aredetermined from signal features. These values are compared with athreshold or a threshold function, and if they exceed this threshold,the restraint arrangement, apparatus or structure, e.g. a pyrotechnicalbelt pretensioner or a first or second-stage airbag, is activated. Inthe case of vehicles having a sensor for measuring impact speed, thisthreshold may be selected as a function of the impact speed. Thecharacteristic of the threshold function depends on the vehiclecharacteristic. A grid lying in the speed activation time plane isneeded to be able to establish the threshold function. Points of thegrid are used as data points via which the threshold values arespecified. This grid results from the activation characteristicsexplained in the following for certain speeds, the speed being 15, 20,25, . . . , 70 km/h, for example.

As shown above, the activation characteristics are determined by linearregression lines in the currently used system. These lines result fromthe activation time required by the vehicle manufacturer for a performedcrash test. The linear regression lines effectively describe therequired activation performance in the speed range in which the crashtests are performed. Described less effectively is the performance inthe higher speed range, i.e. for speeds between 70 and 130 km/h, and forquick, very hard crashes when the regression line provides very shortactivation times, e.g. less than 5 ms.

The activation performance in these crash situations is described betterfor example by a 1/x function or by an exponentially decreasingfunction. A regression analysis may be performed for these functions forcrash types having numerous crash tests just like for the linearfunction. A disadvantage of these functions compared to the linearfunction may be that these functions may not be generalized aseffectively for crash types having fewer crash tests.

The exemplary embodiment and/or exemplary method of the presentinvention provides for a vehicle-dependent speed limit G after which thelinear regression line no longer effectively describes the activationperformance of the airbag. In addition, there is a vehicle-dependentspeed P starting at which the restraint arrangement, apparatus orstructure is either activated at a fixed early instant or is notactivated without detailed differentiation between the different crashtypes. The exemplary method described here provides for the transfer ofthe activation performance from the knowledge of the activationperformance in the lower speed range to the speed range between speedlimit G and speed P.

FIG. 1 shows a block diagram of the exemplary device of the presentinvention. An environment sensor 1 is connected via a first data inputto a control unit 3. An acceleration sensor 2 is also connected tocontrol unit 3 at a second data input. Control unit 3 is assigned aprocessor 4, on which an algorithm for calculating the activation timesof a restraint arrangement, apparatus or structure runs. Additionalalgorithms for controlling other restraint arrangements may also beprocessed. Control unit 3 is connected via a data output to restraintarrangement, apparatus or structure 5. The restraint arrangement,apparatus or structure 5 may include for example airbags, beltpretensions, or a rollover bar and thus form the restraint system.

Restraint arrangement, apparatus or structure 5 may be controlled eitherby control unit 3 or by a further control unit for the restraintarrangement, apparatus or structure. Only one environment sensor 1 andone acceleration sensor 2 are mentioned here as examples. However, morethan one environment sensor and more than one acceleration sensor may beused. Environment sensor 1 is a radar sensor or an ultrasound sensor oran optical sensor, for example. Acceleration sensor 2 is used as animpact sensor that determines the acceleration resulting from theimpact.

The exemplary method represented in the following for determining theactivation characteristics is the basis for the algorithm running incontrol unit 3. This method requires that the activation characteristicsvalid for the lower and middle speed range be given with respect to thecrash type in question. There is a vehicle-dependent limit G after whichthe linear activation characteristics only insufficiently describe theactivation performance for higher speeds. The position of limit G alsodepends on the crash type. Therefore, it may be represented as astraight progression or as any other mathematical function in the speedactivation time plane. For example, the limit may be selected such thatit is essentially above the crash tests performed by the vehiclemanufacturer.

The linear activation characteristics effectively describe theactivation performance for speeds below this limit. There is also avehicle-dependent speed V_(max), starting at which the restraintarrangement, apparatus or structure to be controlled is either activatedat a fixed, early instant or is not activated regardless of the crashtype. Starting at this speed V_(max), there is therefore only thisinstant T_(max) for the activation decision and no real time interval asfor lower speeds. The activation characteristics for every crash typemay be specified for the speed range between this point P_(max) andpreviously described limit G as follows for example: A line is selectedbetween P_(max) and point of intersection S_(Crash-Type). PointS_(Crash-Type) results as the point of intersection between limit G andthe activation characteristic in the lower speed range for the crashtype in question.

Knowledge extracted from the crash test data is represented in theactivation characteristics from the lower speed range. Since theactivation characteristics are used to define points of intersectionS_(Crash-Type), the knowledge extracted from the crash tests isgeneralized for the top speed range. In addition, this sectionallylinear approach allows the activation characteristics to also begeneralized for crash types having fewer available crash tests.Moreover, this sectional approach has the advantage that the activationcharacteristics are selected to be steeper for the higher speed rangethan for the lower one. As a result, the characteristic curvecorresponds better with the ideal, initially steep, then flatter curve.Therefore, the exemplary method of the present invention represents anoptimum compromise between the transferability to other crash types andthe quality of the description of the activation performance.

FIG. 2 uses a speed activation time diagram to show the regression linesthat describe the activation characteristics and are determined indifferent crash tests. The activation time is plotted in ms on theabscissa while the impact speed is indicated in km/h on the ordinate.Three linear regression lines drawn through measuring points for crashtests are shown here. Starting at limit 201, the activationcharacteristics defined by the regression lines are no longer validsince the impact speed here is such that there are other properties.Significantly shorter activation times are to be provided in this case.

FIG. 3 uses another speed activation time diagram to show the use of theimpact speed values according to the exemplary embodiment and/orexemplary method of the present invention to control the activationperformance accordingly. The activation time is plotted in ms on theabscissa while the impact speed is indicated in km/h on the ordinate.Three regression lines 301, 302, 303 are specified for three accidenttypes. As soon as they intersect curve G, which defines the speed limitafter which these regression lines no longer describe the requiredactivation performance with sufficient accuracy, the slope of theindividual regression lines changes. The slope changes such that theymeet at point P_(max), which lies at 130 km/h in this instance, andafter this speed a fixed activation time is provided. The range betweenspeed limit G and point P_(max) for the individual regression lines mayalso be interpolated by other curves, which then however entails greatercalculational effort. The left regression line describes the earliestactivation characteristic while right regression line 301 indicates thelatest activation characteristics.

1-4. (canceled)
 5. A method for activating a restraint system in avehicle, the method comprising: activating the restraint system as afunction of an activation characteristic and at least one quantityderived from an acceleration signal; wherein the at least one quantityexceeds a threshold function that is set as a function of an impactspeed and a required activation time, and wherein a particularactivation characteristic for an accident type runs linearly with afirst slope to a first impact speed value and runs with at least onesecond slope between a first impact speed value and a second impactspeed value, the first impact speed value and the second impact speedvalue depending on a particular vehicle type.
 6. The method of claim 5,wherein the activation characteristic between the first impact speedvalue and the second impact speed value runs linearly.
 7. The method ofclaim 5, wherein a fixed activation time is used starting at the secondimpact speed value.
 8. The method of claim 6, wherein a fixed activationtime is used starting at the second impact speed value.
 9. A device foractivating a restraint system in a vehicle, comprising: an activatingarrangement to activate the restraint system as a function of anactivation characteristic and at least one quantity derived from anacceleration signal; wherein the at least one quantity exceeds athreshold function that is set as a function of an impact speed and arequired activation time, and wherein a particular activationcharacteristic for an accident type runs linearly with a first slope toa first impact speed value and runs with at least one second slopebetween a first impact speed value and a second impact speed value, thefirst impact speed value and the second impact speed value depending ona particular vehicle type.
 10. The device of claim 9, wherein theactivation characteristic between the first impact speed value and thesecond impact speed value runs linearly.
 11. The device of claim 9,wherein a fixed activation time is used starting at the second impactspeed value.
 12. The device of claim 10, wherein a fixed activation timeis used starting at the second impact speed value.